Safety Analysis of Fence Installation on a Large Power Station Concerning Inductive and Conductive Coupling from Nearby Transmission Lines

J. Ma, H. Zhao, and F. P. Dawalibi

Asia-Pacific Power and Energy Engineering Conference (APPEEC2011), Wuhan, P. R. China, March 25 - 28, 2011.

Abstract: This paper presents a safety analysis during the installation of a fence surrounding a large power station under construction. The safety concerns are due to both inductive and conductive coupling from nearby existing transmission lines during steady state and fault conditions. The fence must be installed during the station construction phase and before the installation of its grounding system. Different scenarios are analyzed to ensure the safety during and after the installation of the fence. Based on the analysis, procedures for installing the fence to ensure safety at all times are developed. The analysis and the procedures presented in this paper can be used as a guide when carrying out safety analysis of fence installation under similar circumstances.

Inadequacies of the Industry-Standard IEEE C37.99-2000 Concerning Grounding Neutrals of Shunt Capacitors in High-Voltage Substations

F.P. Dawalibi, S. Tee, S. Fortin and N. Grignon 

IEEE Transactions on PWRD, Vol. 26, No. 2, April 2011, pp. 782-789.

Abstract: The industry-standard IEEE C37.99-2000 recommends the use of Peninsula Neutral Ground as the preferred method to ground the neutrals of capacitor banks in high-voltage substations. The basis for this recommendation is a 1972 IEEE paper by Rogers and Gillies that has remained unchallenged until now. Many grounding designs are carried out according to this approach despite the fact that it is the least efficient one. As long as this IEEE standard is not updated to reflect the new findings reported in this paper, designers will continue to be misguided. In this paper, we demonstrate that IEEE standard C37.99-2000 recommendations have no valid scientific basis by comparing the overall performance of a 735/230-kV substation grounding system designed according to the Peninsula Neutral Ground method, the single-point neutral ground and a more conventional design consisting of reasonably dense ground conductors in the 230-kV capacitor banks area and conclude that the conventional design offers superior performance from a safety and electromagnetic-interference perspective based on the fundamental frequency and full frequency spectrum of the back-to-back capacitor switching transient current discharge.

Advanced Grounding System Analysis for a Large Substation Accounting for Aboveground Bus Bars

J. Liu, F. P. Dawalibi and J. Ma

The International Conference on Electrical Engineering (ICEE 2011), Hong Kong, July 10 - 14, 2011.

Abstract: This paper presents advanced grounding analysis methods and design techniques used to model and analyze a large substation grounding system. This paper is specifically concerned with the effects of the inductive coupling between aboveground bus bars and ground conductors. Computation results for a realistic case are presented by comparing four grounding analysis approaches, namely, a conventional method that assumes an equipotential grid, a method that accounts for voltage attenuation along grid conductors, a method that accounts for both conductor attenuation and circulating currents in the grid, and finally, the exact method that takes into account grid conductor attenuation, grid circulating currents and aboveground bus bars as well. The study demonstrates that in a large substation grounding system buried in low resistivity soil and with high magnitudes of circulating currents, it is necessary to model accurately circulating currents from local sources as well aboveground bus bars in order to accurately account for electromagnetic coupling between conductors and determine touch and step voltages realistically.

Practical and Realistic Considerations of Fault Current Analysis

Y. Li and F. P. Dawalibi

The International Conference on Electrical Engineering (ICEE 2011), Hong Kong, July 10 - 14, 2011.

Abstract: Practical and realistic considerations for fault current split calculations used in power system grounding studies are presented. Scenarios, such as modeling transformers to account for local circulating fault currents, analyzing underground distribution cables, considering tower line faults, and estimating the return currents to remote source contributions by means of shield wires, cable sheaths, etc., are analyzed. It is shown that fault current going into the grounding system and the grounding grid safety evaluation can be overestimated or underestimated if the actual situation is not modeled correctly or considered with the appropriate parameters. Proper analysis of various fault scenarios involving circulating currents, line fault, and underground cables is also presented. The topics discussed in this paper can provide advanced guidelines and references for power engineers to carry out fault current distribution calculations accurately and therefore avoid inappropriate designs in grounding studies.

Analysis and Mitigation for Pipeline Safety and Integrity near Electrical Power Systems

J. Liu and F. P. Dawalibi

The International Conference on Electrical Engineering (ICEE 2011), Hong Kong, July 10 - 14, 2011.

Abstract: Electromagnetic interference caused by electrical power systems on neighboring utilities such as oil, gas, and water pipelines is always a serious concern. Electromagnetic interference issues must be carefully studied at the power system planning stage to make sure that public safety and pipeline integrity are ensured. In this paper, we focus on the proximity effects of a power substation to a nearby pipeline and consider several key variables in order to understand and illustrate the issues related to electromagnetic interference. Typical variables studied consist of the type of bonding between the substation and the pipeline, separation distance between the substation and pipeline, coating of the pipeline, soil models and characteristics and relative position of the power lines and pipelines. Results obtained based on an extensive set of studies are summarized. All charts, observations, and computation results offer useful clues to a better understanding of the electromagnetic influence of power systems on neighboring  pipelines.

Recent Advances in the Modeling and Mitigation of AC Interference along Transmission Lines Right of Ways

Y. Li, F. P. Dawalibi and H. Zhou

NACE Corrosion Shanghai 2011 Conference & Expo, Shanghai, China, October 12 - 14, 2011.

Abstract: Electromagnetic interference between electric power lines, pipelines, railways and communication lines or other metallic circuits can cause serious damage to utilities and may pose safety hazards to the public. The design of mitigation measures to reduce AC interference levels in a pipeline is a relatively straightforward matter when the mitigation can be installed with the pipeline in the same trench. The computation of interference effects along a long and congested right-of-way is a complex and time-consuming procedure, particularly when the soil structure varies along the right of way. This paper introduces and discusses recent advances in the modeling and mitigation of AC interference in pipelines using an integrated hybrid method based on nodal circuit analysis and extended grounding analysis coupled with ground impedance correction techniques to account for soil structure changes along the right of way. Practical examples are examined and results obtained using this approach are presented and compared with those obtained this impedance correction technique. It is shown that the improved integrated method can be applied to provide accurate interference levels which could not be obtained before, resulting in more appropriate mitigation measures.

Seasonal Soil Resistivity Variations at Power Substations Located in Warm Regions

S. Wei, S. Fortin and F. P. Dawalibi

2011 International Conference on Power and Energy Engineering (CPEE2011), Shanghai, China, October 28 - 30, 2011.

Abstract: In warm regions, soil water content is the major timedependent subsurface variable that affects the DC resistivity of the soil. This paper first reviews some fundamental technical information regarding the relationship between soil resistivity and soil moisture, and then describes calculations of shallow resistivity variations due to changes in moisture content. For a given soil texture, an effective medium model is used to obtain fast estimates of soil resistivity for any water saturation level based on a single known resistivity value at a given water saturation level.

Effect of Site Improvement on the Performance of Substation Grounding Systems

J. Ma and F. P. Dawalibi

2011 International Conference on Power and Energy Engineering (CPEE2011), Shanghai, China, October 28 - 30, 2011.

Abstract: The effect of site improvement on the performance of the grounding system of a substation is studied in this paper. The site improvement referred to here is usually implemented by adding soil on top of the existing earth surface. When the added soil has the same resistivity as the local soil resistivity or lower, the touch and step voltages will be lower compared with the case of no site improvement. However, a steeper slope of the side surfaces of the soil volume can make the step voltage higher. When the resistivity of the added soil is higher than the local soil resistivity, both the touch and step voltages are larger compared with the case of no site improvement. An approximate method for modeling the added soil volume on top of a multilayer soil is also presented. The method can be applied to the design and analysis of grounding systems in new substations and power plants when site improvement is required.

Electrostatic Field and Potential Generated by Arbitrarily-Oriented Line and Surface Sources with Additional External Electric Fields in Air

H. Zhao, S. Fortin and F. P. Dawalibi

2011 International Conference on Power and Energy Engineering (CPEE2011), Shanghai, China, October 28 - 30, 2011.

Abstract: This paper presents a new numerical method to calculate the electrostatic field and potential generated by arbitrarily-oriented line and surface sources with additional external electric fields in air. In the analysis, the soil is simplified as a semi-infinite metallic medium. The metallic objects can be connected to ground to keep them at zero potential or can be floating with a known energized potential or leakage current. This approach can be used to simulate the electric field and potential distribution around substations, power plants, transmission line towers, or buildings under a huge charged cloud in extreme conditions, in order to investigate lightning protection scenarios. The electric field generated by the charged cloud can be represented by an external electric field in this type of simulation. In the paper numerical results are presented for various configurations such as conductor systems, parallel plates, multiple plates forming a closed box and a complex system simulating a substation including bus bars, metallic supports and lighting protection masts under a huge charged cloud. Typical results are validated with  available analytical methods or valid numerical methods.

Transient Voltages across Anti-Seismic Foundation Dampers in a Tokamak Building Hit by Lightning

F. Grange, S. Journet, F. P. Dawalibi, S. Fortin and Y. Li

2011 International Conference on Power and Energy Engineering (CPEE2011), Shanghai, China, October 28 - 30, 2011.

Abstract: The ongoing international tokamak (nuclear fusion) demonstration project (ITER) will be housed in a building supported by a 17 m deep complex seismic isolation pit. This 120 m long and 90 m wide pit will house the anti-seismic foundations of the future tokamak Complex. Damage to the anti-seismic foundation structures due to repeated lightning strikes is a major concern and must be prevented by adequate lightning bonding and grounding mitigation measures. This paper describes the results of a detailed study of the response of the tokamak building   structures and associated anti-seismic pit foundations structures to lightning strikes.

Fast 3D Direct Lightning Shielding Protection Computation Methods

Q. Xie, S. Baron, S. Fortin and F. P. Dawalibi

7th Asia-Pacific International Conference on Lightning (APL 2011), Chendu, China, November 1 - 4, 2011.

Abstract: The two EGM based direct lightning shielding methods presented in IEEE Standard 998 are the rolling sphere method and the revised EGM Method. The application of the rolling sphere method described in the IEEE Standard is using 2D drawings to simulate the 3D space environment and is limited to using the same strike distance for all objects in the system. The SBSHLD program based on the revised EGM is an analytical approach which is restricted to some special configurations of masts or shield wires. This paper presents a fast 3D computer program based on the EGM using a collection surface method. It yields identical results to those obtained using the rolling sphere method and can apply to any shape of structure or substation. It can also use different strike distances to horizontal or vertical objects. The example 69kV substation described in IEEE Standard 998 is used to  demonstrate usage of this program.

Calculation of the 'Field Intensification Factors' using Method of Moments for Lightning Protection

H. Zhao, S. Fortin and F. P. Dawalibi

7th Asia-Pacific International Conference on Lightning (APL 2011), Chendu, China, November 1 - 4, 2011.

Abstract: This paper presents a fast and efficient way to calculate the ‘field intensification factors’ which can be used to assess the effectiveness of lightning rods for the protection of structures or to determine the likely lightning attachment points such as the corners and edges of structures and lightning rods. The approach allows for the three-dimensional calculation of the electric field around structures of complex shapes, represented by metallic plates and cylindrical conductor elements. Examples are given for various shapes and dimensions of typical structures, including lightning rods and composite structures. The effect on the field intensification factor of the geometry of the  structure and of the rod dimensions and locations is investigated.

Transient Ground Potential Rises at a Nuclear Fusion Experimental Power Plant Hit Directly by a Lightning Strike

W. Ruan, S. Fortin, F. P. Dawalibi, F. Grange and S. Journet

7th Asia-Pacific International Conference on Lightning (APL 2011), Chendu, China, November 1 - 4, 2011.

Abstract: Electric substations are often exposed to lightning strikes. When that happens, very fast large transient voltage stresses occur. Surge limiters can be destroyed and electronic equipment inside control rooms can be damaged. In order to develop appropriate mitigations that prevent such catastrophic damages, a model of a lightning strike hitting a shielding structure of a substation feeding an experimental nuclear fusion facility (Tokamak) is analyzed. Transient Ground Potential Rises (TGPR) of the substation are studied using an electromagnetic field approach. The system analyzed consists of a detailed model of the grounding system of the substation as well as a skeleton of the power plant grounding system. The effects of the soil resistivity on the TGPR are studied. It is shown that the transient GPR increases when the soil resistivity increases. When the soil resistivity is low, there is little difference in the transient GPR between the substation grounding system alone and the substation grounding system interconnected to the power plant grounding system. However, when the soil resistivity is high enough, the interconnected grounding system between the substation and the power plant can significantly reduce the transient GPR in the substation control room in both its magnitude and its extent over time. Consequently, stress voltages on  electronic equipment  inside the substation control room can be greatly reduced.

Investigation of Transient Voltages in a Tokamak Building Hit by Lightning

F. Grange, S. Journet, F. P. Dawalibi, S. Fortin and Y. Li

7th Asia-Pacific International Conference on Lightning (APL 2011), Chendu, China, November 1 - 4, 2011.

Abstract: The ongoing international Tokamak (nuclear fusion) demonstration project (ITER) will be housed in a building supported by a 17 m deep complex seismic isolation pit. This 120 m long and 90 m wide pit will house the anti-seismic foundations of the future Tokamak Complex. Safety to persons in contact with the building and damage to the anti-seismic foundation structures due to repeated lightning strikes is a major concern and must be prevented by adequate lightning bonding and grounding mitigation measures. This paper describes the results of a detailed study of the response of the Tokamak building structures and associated anti-seismic pit foundations structures to lightning  strikes. This paper focuses on the transient response and related safety aspects.